Activated charcoal, also known as activated carbon, is a form of carbon that has been processed or ‘activated’ to make it extremely porous, such that it has a very large surface area and pore volume available for adsorption, or chemical reactions. For example, due to its high degree of porosity, one gram of activated charcoal has a surface area in excess of 500 m2/g, and in some cases more than 2000 m2/g, and a combined meso and micro pore volume of more than 0.40 cm3/g. These characteristics can be determined by the Brunauer-Emmet-Teller (BET) method using nitrogen gas adsorption.
Activated charcoal can be used in water filters, such as for aquaria, or in air purification. Other uses for activated carbon include large-scale purification of potable water, adsorption of toxic materials from incinerator flue gas streams, and environmental remediation. A number of growth areas in electronics applications also use activated carbons, including electrodes for super capacitors, ultracapacitors, pseudocapacitors and electrochemical storage devices, such as lithium ion batteries. In the health industry, activated carbons are used to combat food poisoning and stomach upsets. In food processing, activated carbons are used to remove impurities from beverages and sugar syrup, for example.
Usually, activated charcoal is produced from low mineral carbonaceous precursor materials, such as wood, coal, or charcoals derived from coconut shells, nutshells and rice husks. The subsequent process of activation requires that the precursor materials are heated at high temperatures sometimes exceeding 1000° C. in the presence of exogenously added activating (i.e. oxidising) agents, such as carbon dioxide, oxygen, acids or superheated steam for several hours. Accordingly, known methods for producing activated charcoal involve the use of externally applied oxidising agents combined with very high activating temperatures for prolonged periods of time. Hence, these methods are reliant on the input of large amounts of energy and the addition of externally applied activating agents, and are therefore very expensive to carry out.
Furthermore, a major difficulty with using chemical activation processes is that it is very difficult to achieve a uniform distribution of the activating agent (e.g. dehydrating/oxidising agent) within the precursor material before treatment. As a result, in current methods for producing activated charcoal, the precursor material must be finely ground down, which is an expensive and time-consuming process, in order to achieve good mixing with the activation agent. There is therefore a requirement to provide a method for preparing activated charcoal which avoids the need to carry out these costly grinding steps prior to activation.